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Author Topic: Treating rust looking breaks in patina  (Read 206 times)

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Offline Ken W2

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Treating rust looking breaks in patina
« on: July 18, 2021, 09:55:34 am »

Hello all: Here is an Aurelian Genio Ant I just finished mechanical cleaning on yesterday (19.09 mm 2.82 gr. Can you believe that in 270 even silver washed that little thing was accepted as the equivalent of two silver denarii issued 100 years earlier likely weighing 6-7 grams and being 90% plus silver, but I digress) and an VRBS ROMA she wolf coin I’m still working on. Both have rust looking breaks in the patina—just in front of the face on the Ant and in several areas on the VR. These breaks were already there when I started, but grew a little as I cleaned around them, mostly on the VR coin. If these breaks showed clean, bare bronze this would be an easy call— live with it and let it darken naturally or touch it up with Jax or LOS— depending on the camp you’re in. I have been leaving these type spots alone and just waxing over after final cleaning and drying.  But is there a chemical treatment that won’t harm the patina but will remove or harden/darken these “rust” spots ? If this was an iron Civil War artifact the last step before waxing would be a phosphoric acid wash which effectively treats any remaining small rust spots or flash rust. But acid not an option with these bronze coins. Any ideas how to treat these “rust” spots?
Ken

Offline Ken W2

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Re: Treating rust looking breaks in patina
« Reply #1 on: July 18, 2021, 11:28:14 am »

CORRECTION:  That a FIDES MILITVM reverse Ant. I confused it with a Severus I’m working now too.

Offline Ron C2

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Re: Treating rust looking breaks in patina
« Reply #2 on: July 18, 2021, 03:57:08 pm »
In my opinion, if you are going to Ren wax them, I'd dry them well and use the wax. That's it.
My Severan Denarii Gallery: Click here

R. Cormier, Ottawa

Offline otlichnik

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Re: Treating rust looking breaks in patina
« Reply #3 on: July 19, 2021, 04:55:02 pm »
Ken,

These are not rust spots and have nothing to do with Fe.

The can be caused by two things.  A layer of the green oxidized AE suffice breaks off revealing metal underneath which then begins to oxidize, but is "behind" in the process.  Or, a spot where a BD reaction has stopped resulting in a rust-colored blister.

The VRBS ROMA looks like the former - the surface has broken through.

The Aurelian might be the latter - arrested BD - hard to tell from the image.

SC
SC
(Shawn Caza, Ottawa)

Offline Ken W2

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Re: Treating rust looking breaks in patina
« Reply #4 on: July 19, 2021, 06:55:46 pm »

Thanks fellows.

Shawn, I assumed it was not iron related rust-- while there probably is some trace iron in the alloy it's likely not enough to cause real rust to this extent.  But, if I knocked a little of the green layer off either coin there would be this rust colored layer beneath it too. (That's how these spots grew from smaller ones initially).  It's like there is a layer of corrosion underlying the green layer.  I think I'll try a soak in a 5% sodium sesquicarbonate on the VRBS ROMA and just see what happens-- I'd like it to be darker and not rust looking.  I don't think that will do any harm, and if it does it won't be any great loss. Thanks again.

Ken 

Offline Ron C2

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Re: Treating rust looking breaks in patina
« Reply #5 on: July 19, 2021, 07:20:47 pm »

Thanks fellows.

Shawn, I assumed it was not iron related rust-- while there probably is some trace iron in the alloy it's likely not enough to cause real rust to this extent.  But, if I knocked a little of the green layer off either coin there would be this rust colored layer beneath it too. (That's how these spots grew from smaller ones initially).  It's like there is a layer of corrosion underlying the green layer.  I think I'll try a soak in a 5% sodium sesquicarbonate on the VRBS ROMA and just see what happens-- I'd like it to be darker and not rust looking.  I don't think that will do any harm, and if it does it won't be any great loss. Thanks again.

Ken

Ken,

The color is basically raw bronze powder and flake that has come loose from the fabric of the coin because of the spalling effect the green patina had on the coin itself when it formed. In essence, a chemical reaction is forming malachite mineral on the coin's surface and dissolving some of the bronze in the process.  This is why if you treat a patinated coin with diluted lye to remove the patina, the underlying flan is more porous than a smooth green patina.

Anything that darkens those exposed bronze areas will risk removing more patina, in my view. If you wax the coin, they will slightly darken anyhow. Personally, I would accept the coins as they are. Other work is likely to not improve them, but YMMV.
My Severan Denarii Gallery: Click here

R. Cormier, Ottawa

Offline Virgil H

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Re: Treating rust looking breaks in patina
« Reply #6 on: July 20, 2021, 11:21:36 pm »
I am no expert, but, seems to me that coins I have that have these kinds of issues would just get worse if I tried to get them off. Unless I am not seeing your images properly, these areas already have outer layers removed and in fact what the "rust" is is already gone. Unless there is a reason, I just leave this stuff as trying to take it off makes matters worse. I personally have never used wax, but maybe that would make it look better. I like coins as they are, though, to me wax is an unnatural manipulation that I don't want.

Virgil

Offline Ken W2

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Re: Treating rust looking breaks in patina
« Reply #7 on: July 26, 2021, 09:16:39 am »

Just to follow up, I treated the VRBS ROMA coin with sodium sesquicarbonate soak over the week end. Didn't help or hurt.  I'll just dry in my usual fashion-- overnight alcohol soak, then a warm oven, then wax.   

Ken

 

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